This invention relates generally to inflatable passive restraint systems for use in vehicles for restraining the movement of a seated occupant such as in the event of a collision. More particularly, the invention relates to an improved airbag module assembly especially suited for driver side occupant protection.
It is well known to protect a vehicle occupant using a cushion or bag, e.g., an “airbag cushion,” that is inflated or expanded with gas such as when the vehicle encounters a sudden deceleration, such as in the event of a collision. In such systems, the airbag cushion is normally housed in an uninflated and folded condition to minimize space requirements. Upon actuation of the system, the cushion begins to be inflated in a matter of no more than a few milliseconds with gas produced or supplied by a device commonly referred to as an “inflator.”
Vehicular inflatable restraint systems generally include multiple crash sensors generally positioned about or mounted to the frame and/or body of the subject vehicle and serve to sense sudden decelerations by the vehicle. In turn, upon activation, one or more of the sensors sends a signal to an airbag module assembly strategically positioned within the riding compartment of the vehicle to actuate deployment of the airbag. In practice, such an airbag cushion is desirably deployed into a location within the vehicle between the occupant and certain parts of the vehicle interior, such as a door, steering wheel, instrument panel or the like, to prevent or avoid the occupant from forcibly striking such part(s) of the vehicle interior.
An airbag module assembly provided for the protection of a vehicle driver, i.e., a driver side airbag module assembly, is typically mounted in a storage compartment located along the steering column of the vehicle. In airbag module assemblies, it is common for the airbag cushion and, at least a portion, of the associated inflator device to be stowed or contained within a module housing such as composed, at least in part, by a housing member such as in the form of a canister. Such a housing member component typically has joined or connected therewith an associated or corresponding cover member or element.
As will be appreciated, the inclusion of such a cover member can be desirable in various respects. For example, such a cover member may desirably serve to enclose various of the respective module assembly components such as to prevent damage thereto, such as damage to the airbag cushion. Further, it has become common to provide for the inclusion of such a cover member as a decorative feature such as forms a part of the steering wheel or vehicle interior trim. Such cover members typically include a frangible section, such as having tear seams or lines of reduced thickness such as to more readily permit one or more sections of the cover member to move upon system actuation such as to permit the associated airbag cushion to expand past the cover upon inflation.
Unfortunately, the inclusion of such tear seams or lines of reduced thickness in a cover member can present undesirable cosmetic or appearance problems. For example, such tear seams or lines of reduced thickness can produce or result in undesired show through (e.g., where shapes or features on the backside of the cover member can be relatively easily discerned from a viewing of the front side of the cover member), sink marks (e.g., where the cover member has an undesired, lower or uneven outer surface), or glossing (e.g., where additives in the material for forming the cover material undesirably separate and accumulate at the surface of the cover material during manufacture, resulting in a “glossy” finish), can result from processing. For example, when a cover member is prepared by molding fabrication of a thermoplastic elastomer, an uneven shrinkage of the cover material upon processing can result in show through, sink marks and/or glossing. Such uneven shrinkage can, for example, occur as a result of the item being processed having relatively widely varying thicknesses and thus varying processing time and condition requirements.
In practice, the frangible section of such cover members must be sufficiently strong to resist accidental opening prior to proper actuation of the restraint system. Consequently, the frangible sections of such cover members generally require the proper application of a relatively large force onto the cover, such as by the inflating airbag cushion, before the frangible section releases and permits the airbag cushion to deploy therethrough.
The application of such large forces may, however, create a risk that the cover or at least a portion thereof may undesirably become dislodged or unattached from the associated housing member. In order to reduce, minimize or eliminate the risk of such dislodgement or detachment, a need and a demand has existed for a cover attachment arrangement wherein the cover is securely attached to or with the module housing. Unfortunately, the need for strength in the connection between an associated cover and housing has often resulted in more complicated than desired connection schemes. For example, in order to ensure proper cover attachment and retention, common cover and housing connection schemes have incorporated or relied on the inclusion of one or more of the following features:                1) various secondary components, such as rivets or other fasteners or the like;        2) various secondary operations, such as crimping or the like;        3) relatively intricate or complicated shapes or forms; and        4) tethering of the opening cover member to the housing.        
Furthermore, the inclusion of such features may typically undesirably increases the costs associated with the connection scheme. Further, the inclusion of such features typically undesirably complicates or makes more expensive the rework of such installations. For example, the rework of such designs is typically laborious and may require scrapping of one or more components involved in the rework.
Thus, there is a need and a demand for an improved airbag module assembly such as may desirably minimize or, preferably, avoid the use of tear seams or lines of reduced thickness in a cover member and thus preferably minimize or avoid the cosmetic or appearance problems commonly associated therewith. Further, there is a need and a demand for an improved airbag module assembly such as may more readily and easily permit or provide positive cover attachment throughout the deployment process and do so in a relatively simple, effective and efficient manner. In particular, there is a need and a demand for an improved airbag module cover attachment arrangement which more readily and easily permits or provides positive cover attachment throughout the deployment process without incorporating or relying on the inclusion of one or more of the following features:                1) secondary components, such as rivets or other fasteners or the like;        2) secondary operations, such as crimping or the like;        3) relatively intricate or complicated shapes or forms; and        4) tethering of the opening cover member to the housing.        